Ovulation is the release of a single, mature egg from a follicle that developed in the ovary. It usually occurs regularly, around day 14 of a 28-day menstrual cycle. Once released, the egg is capable of being fertilized for 12 to 48 hours before it begins to disintegrate. This is the most fertile period of your cycle: during ovulation your chances of conception are highest.

When does ovulation occur?

Ovulation usually takes place 14 days after the beginning of your menstrual cycle. The time of ovulation within the menstrual cycle is determined by the luteal phase, which is usually 12 to 16 days long. You can calculate the time of ovulation within your cycle by subtracting the length of your luteal phase from the length of your cycle. For example, if your cycle is 28 days long and your luteal phase is 12 days long, the ovulation will occur on day 16 of your cycle (28-12=16). The exact time of ovulation may vary within your cycle, because ovulation can be delayed by a number of factors such as stress, illness, diet, or increased physical activity.

How does ovulation determine my fertile days?

Your fertile period starts about 4-5 days before ovulation, and ends about 24-48 hours after it. This is because sperm can live in your body for approximately 4 to 5 days, and the egg can live for 24 to 48 hours after being released. You are most fertile on the day before and the day of ovulation. Knowing your fertile days can help you increase your chances of getting pregnant, or avoid an unwanted pregnancy. Read Ovulation and Pregnancy and Ovulation and Contraception for more information.